Ceramic composite material for optical conversion and use thereof

ABSTRACT

A ceramic composite material for light conversion, which is a solidified body comprising two or more matrix phases with respective components being two or more oxides selected from the group consisting of metal oxides and complex oxides each produced from two or more metal oxides, wherein at least one of the matrix phases is a phosphor phase containing an activated oxide. The solidified body is preferably obtained by the unidirectional solidification method. The ceramic composite material for light conversion is excellent in brightness, light-mixing property, heat resistance and ultraviolet light resistance.

TECHNICAL FIELD

The present invention relates to a ceramic composite material, for lightconversion, having a function of converting some irradiated light intolight at a wavelength different from the irradiated light and at thesame time, mixing the converted light with the unconverted irradiatedlight to cause conversion into light having a color tone different fromthe irradiated light, and also relates to the use thereof.

BACKGROUND ART

With a recent practical implementation of a blue light-emitting diode,studies are being aggressively made to develop a white light source byutilizing this diode as the light emission source. White light is invery large demand as a light source for illumination and, in addition,is greatly advantageous in that a light-emitting diode has a low powerconsumption and ensures a long life, compared with existing white lightsources.

According to this method, the blue light emitted from the bluelight-emitting diode is converted into white light by using a materialhaving a light conversion function, in which out of three primary lightcolors, the blue light is included in the light emitted from the bluelight-emitting diode, but green light and red light must be emitted. Forthis purpose, a phosphor capable of absorbing light at a certainwavelength and emitting light at a wavelength different from theabsorbed light is used.

With respect to the method for converting blue light of the bluelight-emitting diode into white light, as described, for example, inJapanese Unexamined Patent Publication (Kokai) No. 2000-208815, acoating layer containing a phosphor capable of absorbing a part of theblue light and emitting yellow light, and a molded layer for mixing theblue light of the light source and the yellow light from the coatinglayer are provided at the front of a light-emitting device. Referring toFIG. 1, a coating layer 2 is present at the front of a light-emittingdevice 1, and a molded layer 3 is further provided thereon. In theFigure, 4 is an electrically conducting wire, and each of 5 and 6 is alead. In this case, color mixing takes place not only in the moldedlayer 3 but also in the coating layer 2.

As for the coating layer employed in conventional techniques, a mixtureof an epoxy resin and a YAG (Yttrium-aluminum-garnet) powder doped witha cerium compound is coated on a light-emitting device (see, Kokai No.2000-208815). However, according to this method, uniform white light canbe hardly obtained with good reproducibility because of difficulty incontrol for, for example, ensuring uniform mixing of the phosphor powderand the resin, or optimizing the thickness of coated film. Also, use ofa phosphor powder having low transparency to light is an obstacle to theproduction of a high-brightness light-emitting diode. Furthermore, heatstorage arises as a problem when high-intensity light is to be obtained,and the heat resistance and the ultraviolet light resistance of resinsfor the coating layer and molded layer become important problems.

In order to overcome these problems, a material of emitting yellow lightby absorbing blue light emitted from the light-emitting diode, and atthe same time, exhibiting excellent light mixing property and high heatresistance is necessary.

An object of the present invention is to provide a ceramic compositematerial not only having a light conversion function, that is, afunction of absorbing light at a certain wavelength and emitting lightat a wavelength different from the absorbed light, but also ensuringhigh brightness and a good light mixing property as well as excellentresistance against heat and ultraviolet light.

DISCLOSURE OF THE INVENTION

The present inventors have found that the above-described object can beattained by a solidified body comprising two or more oxides andcomprising a matrix phase containing a compound of emittingfluorescence. The present invention has been accomplished based on thisfinding.

That is, the present invention provides the followings.

(1) A ceramic composite material for light conversion, which is asolidified body comprising two or more matrix phases with respectivecomponents being two or more oxides selected from the group consistingof metal oxides and complex oxides each produced from two or more metaloxides, wherein at least one of the matrix phases is a phosphor phasecontaining an activated oxide.

(2) The ceramic composite material for light conversion as described in(1) above, wherein the solidified body is obtained by the unidirectionalsolidification method.

(3) The ceramic composite material for light conversion as described in(2) above, wherein respective matrix phases are continuously andthree-dimensionally disposed and entangled with each other.

(4) The ceramic composite material for light conversion as described inany one of (1) to (3) above, wherein the metal oxide is selected fromthe group consisting of Al₂O₃, MgO, SiO₂, TiO₂, ZrO₂, CaO, Y₂O₃, BaO,BeO, FeO, Fe₂O₃, MnO, CoO, Nb₂O₅, Ta₂O₅, Cr₂O₃, SrO, ZnO, NiO, Li₂O,Ga₂O₃, HfO₂, ThO₂, UO₂, SnO₂ and rare earth element oxides (La₂O₃, Y₂O₃,CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Gd₂O₃, Eu₂O₃, Tb₄O₇, Dy₂O₃, Ho₂O₃, Er₂O₃,Tm₂O₃, Yb₂O₃ and Lu₂O₃).

(5) The ceramic composite material for light conversion as described inany one of (1) to (3) above, wherein the complex oxide produced from acombination of two or more metal oxides is selected from the groupconsisting of 3Al₂O₃.2SiO₂ (mullite), MgO.Al₂O₃, Al₂O₃.TiO₂, BaO.6Al₂O₃,BaO.Al₂O₃, BeO.3Al₂O₃, BeO.Al₂O₃, 3BeO.Al₂O₃, CaO.TiO₂, CaO.Nb₂O₃,CaO.ZrO₂, 2CoO.TiO₂, FeAl₂O₄, MnAl₂O₄, 3MgO.Y₂O₃, 2MgO.SiO₂, MgCr₂O₄,MgO.TiO₂, MgO.Ta₂O₅, MnO.TiO₂, 2MnO.TiO₂, 3SrO.Al₂O₃, SrO.Al₂O₃,SrO.2Al₂O₃, SrO.6Al₂O₃, SrO.TiO₃, TiO₂.3Nb₂O₅, TiO₂.Nb₂O₅, 3Y₂O₃.5Al₂O₃,2Y₂O₃.Al₂O₃, 2MgO.2Al₂O₃.5SiO₂, LaAlO₃, CeAlO₃, PrAlO₃, NdAlO₃, SmAlO₃,EuAlO₃, GdAlO₃, DyAlO₃, Yb₄Al₂O₉, Er₃Al₅O₁₂, 11Al₂O₃.La₂O₃,11Al₂O₃.Nd₂O₃, 11Al₂O₃.Pr₂O₃, EuAl₁₁O₁₈, 2Gd₂O₃.Al₂O₃, 11Al₂O₃.Sm₂O₃,Yb₃Al₅O₁₂, CeAl₁₁O₁₈ and Er₄Al₂O₉.

(6) The ceramic composite material for light conversion as described inany one of (1) to (3) above, wherein the phases constituting the matrixare two phases of α-Al₂O₃ phase and Y₃Al₅O₁₂ phase.

(7) The ceramic composite material for light conversion as described inany one of (1) to (6) above, wherein the activating element is cerium.

(8) A light conversion method comprising converting the color of lightemitted from a light-emitting diode into a different color by using theceramic composite material for light conversion described in any one of(1) to (7) above.

(9) A light conversion method comprising converging blue light intowhite light by using a ceramic composite material for light conversion,the ceramic composite material comprising a matrix in which theconstituent phases are an α-Al₂O₃ phase and a Y₃Al₅O₁₂ phase and theY₃Al₅O₁₂ phase is a phosphor activated with cerium.

(10) A light-emitting diode comprising a light-emitting diode chip andthe ceramic composite material for light conversion described in any oneof (1) to (7) above.

(11) The light-emitting diode as described in (10) above, wherein theceramic composite material for light conversion contains a matrix phasecapable of being excited by visible light emitted from thelight-emitting diode chip and emitting fluorescence of visible light ata wavelength longer than the excitation wavelength.

(12) The light-emitting diode as described in (10) or (11) above,wherein the ceramic composite material for light conversion convertsblue light emitted from the light-emitting diode chip into white light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a conventional light-emittingdiode.

FIG. 2 is a cross-sectional view showing an example of thelight-emitting diode of the present invention.

FIG. 3 is an electron microphotograph showing the texture of a materialobtained in an Example.

FIG. 4 is an electron microphotograph showing the structure of the YAGphase in a material obtained in an Example.

FIG. 5 is a spectrum showing fluorescent characteristics of the materialobtained in Example 1.

FIG. 6 is a view roughly showing the method for measuring fluorescentcharacteristics.

FIG. 7 is a view showing detection examples in a detector.

FIG. 8 is a view showing an example of the relationship between thespecimen thickness and the fluorescent characteristics of a lightconverting material.

FIG. 9 is a view showing an example of the relationship between thespecimen thickness and the fluorescent characteristics of a lightconverting material. The scale for light of 530 nm is enlarged.

FIG. 10 is a spectrum showing fluorescent characteristics of thematerials obtained in Example 2 and the Comparative Example.

MODE FOR CARRYING OUT THE INVENTION

In the ceramic composite material of the present invention, a uniformtexture free of colony and voids is provided by controlling theproduction conditions. Also, a grain boundary which is present in ageneral sintered body obtained by pressure-sintering a mixed powderprepared to comprise predetermined components is not present.Furthermore, a ceramic composite material where the oxides or complexoxides constituting the composite material each consists of singlecrystal/single crystal, single crystal/polycrystal orpolycrystal/polycrystal can also be obtained by controlling theproduction conditions. The “single crystal” as used in the presentinvention means a crystal structure in such a state that onlydiffraction peaks from a specific crystal plane are observed by theX-ray diffraction. In addition, the optical property, mechanicalproperty and thermal property may also be changed by dissolving orextracting an oxide other than the constituent oxide to one of thephases constituting the composite material or by presenting it at theinterface.

The ceramic composite material of the present invention has a structurewhere the constituent oxide phases are homogeneously and continuouslyconnected in a micro scale. The size of each phase can be controlled bychanging the solidification conditions. It is generally from 1 to 50 μm.

The ceramic composite material of the present invention is produced bymelting raw material oxides and then solidifying it. For example, thesolidified body may be obtained by a simple and easy method of chargingthe melt into a crucible kept at a predetermined temperature and thencooling and solidifying it while controlling the cooling temperature.The unidirectional solidification method is most preferred. The processthereof is roughly described below.

A metal oxide for forming a matrix phase, and a metal oxide as afluorescent emitter are mixed at a desired composition ratio to preparea mixed powder. The mixing method is not particularly limited and eithera dry mixing method or a wet mixing method can be employed.Subsequently, the mixed powder is heated and melted at a temperaturesufficient to cause the charged raw materials to melt by using awell-known melting furnace such as arc melting furnace. For example, inthe case of Al₂O₃ and Er₂O₃, the mixed powder is heated and melted at1,900 to 2,000° C.

The obtained melt is as-is charged into a crucible and subjected tounidirectional solidification, or after the melt is once solidified, theresulting lump is ground, charged into a crucible and againheated/melted and then the obtained molten liquid is subjected tounidirectional solidification by withdrawing the crucible from theheating zone of the melting furnace. The unidirectional solidificationof the melt may be performed under atmospheric pressure but, to obtain amaterial with fewer defects in the crystal phases, this is preferablyperformed under a pressure of 4,000 Pa or less, more preferably 0.13 Pa(10⁻³ Torr) or less.

The withdrawing rate of the crucible from the heating zone, that is, thesolidification rate of the melt, is set to an appropriate valueaccording to the melt composition. The withdrawing rate is usually 50mm/hour or less, preferably from 1 to 20 mm/hour.

With respect to the apparatus used for the unidirectionalsolidification, a well-known apparatus may be used, where a crucible isvertically housed in a cylindrical container disposed in the verticaldirection, an induction coil for heating is fixed at the exterior of thecylindrical container at the center part, and a vacuum pump fordepressurizing the space in the container is also disposed.

The phosphor constituting at least one matrix phase of the ceramiccomposite material for light conversion of the present invention can beobtained by adding an activating element to a metal oxide or a complexoxide. Such a phosphor material is known and need not be additionallydescribed in particular. In the ceramic composite material for use inthe ceramic composite material for light conversion of the presentinvention, at least one matrix phase is made to function as a phosphorphase, and fundamentally, the ceramic composite material is the same asthose disclosed, for example, in Japanese Unexamined Patent Publication(Kokai) Nos. 7-149597, 7-187893, 8-81257, 8-253389, 8-253390 and 9-67194previously filed by the applicant (assignee) of the present inventionand their corresponding U.S. applications (U.S. Pat. Nos. 5,569,547,5,484,752 and 5,902,763), and can be produced by the production methodsdisclosed in these patent applications (patents). The contents disclosedin these patent applications and patents are incorporated herein byreference.

A block in a required shape is cut out from the resulting solidifiedbody and used as a ceramic composite material substrate of convertinglight at a certain wavelength into light having the objective othercolor hue.

With respect to the oxide species for constituting the matrix phases,various combinations may be employed, but a ceramic selected from thegroup consisting of metal oxides and complex oxides produced from two ormore metal oxides is preferred.

Examples of the metal oxide include aluminum oxide (Al₂O₃), zirconiumoxide (ZrO₂), magnesium oxide (MgO), silicon oxide (SiO₂), titaniumoxide (TiO₂), barium oxide (BaO), beryllium oxide (BeO), calcium oxide(CaO), chromium oxide (Cr₂O₃) and rare earth element oxides (La₂O₃,Y₂O₃, CeO₂, Pr₆O₁₁, Nd₂O₃, Sm₂O₃, Gd₂O₃, Eu₂O₃, Tb₄O₇, Dy₂O₃, Ho₂O₃,Er₂O₃, Tm₂O₃, Yb₂O₃, Lu₂O₃).

Examples of the complex oxide produced from these metal oxides includeLaAlO₃, CeAlO₃, PrAlO₃, NdAlO₃, SmAlO₃, EuAlO₃, GdAlO₃, DyAlO₃, ErAlO₃,Yb₄Al₂O₉, Y₃Al₅O₁₂, Er₃Al₅O₁₂, 11Al₂O₃.La₂O₃, 11Al₂O₃.Nd₂O₃,3Dy₂O₃.5Al₂O₃, 2Dy₂O₃.Al₂O₃, 11Al₂O₃.Pr₂O₃, EuAl₁₁O₁₈, 2Gd₂O₃.Al₂O₃,11Al₂O₃.Sm₂O₃, Yb₃Al₅O₁₂, CeAl₁₁O₁₈ and Er₄Al₂O₉.

For example, in the case of a combination of Al₂O₃ and Gd₂O₃, a eutecticcrystal is formed by Al₂O₃: 78 mol % and Gd₂O₃: 22 mol % and therefore,a ceramic composite material comprising an Al₂O₃ phase and aperovskite-structure GdAlO₃ phase which is a complex oxide of Al₂O₃ andGd₂O₃ can be obtained. Similarly, the fractions of α-Al₂O₃ and GdAlO₃can be changed within the range from about 20 to 80 vol % and from about80 to 20 vol %, respectively. Other examples of the complex oxideproduced from two or more metal oxides and having a perovskite structureinclude LaAlO₃, CeAlO₃, PrAlO₃, NdAlO₃, SmAlO₃, EuAlO₃ and DyAlO₃. Whenany one of these complex oxides constitutes the composite material ofthe present invention, a ceramic composite material having a finetexture and a large mechanical strength can be obtained.

Also, in the case of a combination of Al₂O₃ and Er₂O₃, a eutecticcrystal is formed by Al₂O₃: 81.1 mol % and Er₂O₃: 18.9 mol % andtherefore, a ceramic composite material comprising an Al₂O₃ phase and agarnet-structure Er₃Al₅O₁₂ phase which is a complex oxide of Al₂O₃ andEr₂O₃ can be obtained. Similarly, the fractions of α-Al₂O₃ and Er₃Al₅O₁₂can be changed in the range from about 20 to 80 vol % and from about 80to 20 vol %, respectively. Other examples of the complex oxide producedfrom two or more metal oxide and having a garnet structure includeYb₃Al₅O₁₂. When any one of these complex oxides constitutes thecomposite material of the present invention, a ceramic compositematerial having a high creep strength can be obtained.

Among these, a combination of Al₂O₃ and a rare earth element oxide ispreferred. This is because a material excellent not only in themechanical characteristics but also in the optical characteristics isprovided and also because a composite material in which respectivematrix phases are three-dimensionally and continuously entangled isreadily obtained by the unidirectional solidification method asdescribed later and a matrix phase allowing for stable existence of aphosphor comprising a rare earth metal oxide is formed. In particular, acomposite material comprising Al₂O₃ and Y₃Al₅O₁₂ two matrix phasesproduced from Al₂O₃ and Y₂O₃ is preferred.

The phosphor is obtained by adding an activating element to theabove-described metal oxide or complex oxide.

The activating element (phosphor seed) incorporated into the matrixphase is appropriately selected according to the wavelength of lightsource and the color hue required by converting the color of the lightsource. For example, for converting blue light at 430 to 480 nm of theblue light-emitting diode into white light, it is preferred to usecerium as the activating element and add an oxide of cerium. Of course,the color can be adjusted by adding a plurality of elements, forexample, cerium and another phosphor seed. The activating element exceptfor cerium varies depending on the kind of the matrix oxide but, forexample, terbium, europium, manganese, chromium, neodymium anddysprosium are used.

For adding an activating element (phosphor seed) to the matrix oxidephase, this may be usually attained by adding an oxide of the activatingelement in a predetermined amount.

The ceramic composite material of the present invention comprises a fewkinds of matrix phases and the element added for the activation isconsidered to be existed according to the distribution coefficient andpresent in each matrix phase. The phase of the emitted fluorescencedepends on the components. For example, a composite material comprisingalumina (Al₂O₃) and Y₃Al₅O₁₂ matrix phases is formed from Al₂O₃ andY₂O₃. Fluorescence is emitted from the Y₃Al₅O₁₂ phase and this phase isconsidered to be a cerium-activated phosphor represented by Y₃Al₅O₁₂:Ce.According to the distribution coefficient, the Ce in the composite ismostly existed in the Y₃Al₅O₁₂ phase and scarcely present in the aluminaphase. The phase in which contains the activating elements cannot alwaysbecome a phosphor, cannot be indiscriminately said to become a phosphor,because the formation of a phosphor depends on the components in theceramic composite material of the present invention, at least one matrixphase is a phase for emitting fluorescence.

Each of the alumina and Y₃Al₅O₁₂ is transparent, and the matrix phasecomprising a cerium-activated phosphor represented by Y₃Al₅O₁₂:Ce isalso fundamentally transparent. In the composite material comprisingalumina (Al₂O₃) and Y₃Al₅O₁₂:Ce matrix phases, the blue light enteringand transmitted through the alumina phase is blue light as-is, but apart of the blue light entered the Y₃Al₅O₁₂:Ce phase is changed toyellow light. These lights are mixed in this composite, whereby thetransmitted light appears as a white light.

By the unidirectional solidification method, a composite material havinga structure that respective matrix phases are three-dimensionally andcomplicatedly entangled each other can be obtained (see, for example,FIGS. 3 and 4). Particularly, when Al₂O₃ and a rare earth metal oxideare used, a composite material having such a structure is easilyobtained. This structure is advantageous as a light converting material,because in addition to high transparency of the Al₂O₃ phase, theY₃Al₅O₁₂:Ce matrix phase acts as a uniform phosphor as a whole (theactivating element cerium which predominates the light emission isuniformly distributed in the entire matrix phase on the atomic level).And by virtue of the structure where these phases arethree-dimensionally and complicatedly entangled, high brightness andeffective color mixing of transmitted light and fluorescence arerealized.

Furthermore, in the case of a material obtained by mixing a phosphorpowder and a resin, light scattering occurs on the powder surface, onthe other hand, the composite material of the present invention is freefrom such light scattering so that the light transmittance can be highand the light (blue light) of the light-emitting diode can beefficiently utilized.

In addition, the composite material of the present invention is aceramic material having a high melting point and, therefore, isadvantageous in that the thermal stability is very high and, in turn,the problem of heat resistance as in resin materials does not arise andalso in that the problem of deterioration due to ultraviolet light doesnot occur.

Accordingly, the ceramic composite material of the present invention isa ceramic composite material not only having a conversion function, thatis, a function of absorbing light at a certain wavelength and emittingfluorescence which is light at a wavelength different from that of thelight absorbed, but also being excellent in brightness, lighttransmittance, light mixing property, light usability, heat resistanceand ultraviolet resistance, and this is a ceramic composite material forlight conversion suitably usable for the purpose of converting color ofa light-emitting diode.

In the case of using the ceramic composite material for light conversionof the present invention in a light-emitting diode, the light-emittingdiode may be fabricated, for example, as shown in FIG. 2, by disposingthe ceramic composite material 8 for light conversion of the presentinvention at the front of a light-emitting diode (LED) chip 1. In FIG.2, similarly to FIG. 1, 4 is an electrically conducting wire and each of5 and 6 is a lead. The chip (element) 1 may also be disposed to comeinto contact with the ceramic composite material 8 for light conversion,and this seems to be more preferred in view of heat radiation of theelement. The shape of the container or board can be changed as needed,and the construction material can also be selected as needed.

The present invention is described in greater detail below by referringto specific examples.

EXAMPLES Example 1

An α-Al₂O₃ powder (purity: 99.99%) and a Y₂O₃ powder (purity: 99.999%)were mixed at a ratio of 82:18 by mol and a CeO₂ powder (purity: 99.99%)was mixed to have a ratio of 0.01 mol per mol of Y₃Al₅O₁₂ produced bythe reaction of oxides charged. These powders were wet-mixed in ethanolby a ball mill for 16 hours and, then, the ethanol was removed by usingan evaporator to obtain a raw material powder. This raw material powderwas preliminarily melted in a vacuum furnace and used as a raw materialfor the unidirectional solidification.

The obtained raw material was charged into a molybdenum crucible and,then the crucible was set in a unidirectional solidification apparatus.The raw material was melted under a pressure of 1.33×10⁻³ Pa (10⁻⁵Torr). In the same atmosphere, the crucible was moved down at a speed of5 mm/hour, whereby a solidified body was obtained. This solidified bodytook on a yellow color.

FIG. 3 shows a cross-sectional texture perpendicular to thesolidification direction of the solidified body. The white area is theY₃Al₅O₁₂ (more exactly Y₃Al₅O₁₂:Ce) phase and the black area is theAl₂O₃ phase. It is seen that this solidified body is free from a colonyor a grain boundary phase and has a uniform texture without any thepresence of air bubbles or voids.

FIG. 4 is an electron microphotograph showing the three-dimensionalstructure of the Y₃Al₅O₁₂ phase perpendicular to the solidificationdirection in a sample obtained by cutting out a specimen in the samedirection and heating it together with a carbon powder at 1,600° C. toremove the Al₂O₃ phase in the vicinity of the surface of the specimen.

The X-ray diffraction from the surface nearly perpendicular to thesolidification direction was observed, as a result, only diffractionpeaks assigned to (110) face of YAG and (110) face of α-Al₂O₃,respectively, were observed.

It is seen from these results that in this composite material, twophases of α-Al₂O₃ single crystal phase and Y₃Al₅O₁₂ single crystal phaseare present and these phases are continuously and three-dimensionallydisposed and entangled with each other.

From the solidified body, a 1 mm-thick substrate was cut out in thedirection perpendicular to the solidification direction. The fluorescentcharacteristics of this material were evaluated by a fluorescenceevaluating apparatus. The results are shown in FIG. 5. This material wasfound to have yellow fluorescence having a wide spectrum with a peak atabout 530 nm when blue light at about 450 nm was irradiated.Accordingly, the Y₃Al₅O₁₂ phase is a phosphor represented byY₃Al₅O₁₂:Ce.

Thereafter, the measurement for confirming the mixing property with bluelight was performed by the method shown in FIG. 6. A mirror 14 wasplaced on the lower side of a specimen 13 so that the light transmittedthrough the specimen could return to the detector. When the mirror isarranged in this way, the light reflected from the surface or inside ofthe specimen enters the detector 6. The emitted light 12 used was bluelight at 450 nm from a light source 1. As for the thickness of specimen,four kinds of 0.1 mm, 0.2 mm, 0.5 mm and 1.0 mm were used.

FIG. 7 shows detection examples in the detector. In this Figure, twospecimens differing in the thickness are used and it is seen that as thespecimen thickness increases, the blue light at 450 nm decreases.

FIG. 8 shows the relationship of the specimen thickness with the bluelight intensity and with the yellow fluorescence intensity. As for theyellow fluorescence, FIG. 9 shows an enlarged view by changing the scaleon the ordinate. The blue light intensity decreases as the specimenthickness increases but becomes almost constant at a thickness of 0.5 mmor more. On the other hand, the yellow fluorescence intensity increasesas the specimen thickness increases, and after reaching the maximumvalue, the intensity decreases and similarly to blue light, becomesalmost constant at a thickness of 0.5 mm or more. The reason why themeasured values become constant in the region having a large specimenthickness is because the reflected light of blue light from the specimensurface and the scattered light of yellow fluorescence generated in thephase at a depth less than a certain value from the surface aremeasured. This reveals that, in the case of a thick specimen, theincident light is absorbed in the specimen to cause wavelengthconversion and is not transmitted through the specimen and on thecontrary, in the case of a thin specimen, a part of the incident lightis transmitted through the specimen and reflected on the mirror and apart of the reflected light again comes out from the specimen.

As seen from these observation results, this material transmits theincident blue light and at the same time, converts a part of the bluelight into yellow light having a wide spectrum showing a peak in thevicinity of 530 nm, and these two lights are mixed to emit white light.It is also known that the color can be adjusted by controlling thethickness of the material.

Example 2

From the ceramic composite material for light conversion produced inExample 1, a thin plate was cut out by a diamond cutter. This thin platewas processed to produce a disc-like specimen mountable on alight-emitting diode shown in FIG. 2, and a light-emitting diode wasfabricated. The wavelength of the blue light-emitting diode chip usedwas 470 nm. FIG. 10 shows a light emission spectrum of the thus-obtainedwhite light-emitting diode. Blue light at about 470 nm and light at 530nm emitted from the ceramic composite material for light conversion wereobserved.

Furthermore, the color was measured by placing this light-emitting diodein an integrating sphere. As a result, the color of emitted light hadCIE chromaticity coordinates of x=0.27 and y=0.34 and was verified to bea white color.

Comparative Example 1

Al₂O₃ (purity: 99.99%) and Y₂O₃ (purity: 99.999%) were mixed by themethod described in Example 1 to give a Ce activation amount of 0.03 molper mol of Y₃Al₅O₁₂, and dried to obtain a raw material. Thereto, 5parts by weight of barium fluoride (BaF₂) was mixed as a flux per 100parts by weight of the raw material and the mixture was charged into analumina crucible and fired at 1,600° C. for 1 hour in air. After thecrucible was returned to room temperature, the specimen was taken outtherefrom and washed with a nitric acid solution to remove the flux.Thereafter, 40 parts by weight of the thus Ce-activated YAG powder waskneaded with 100 parts by weight of an epoxy resin, and the resin washardened at 120° C. for 1 hour and at 150° C. for 4 hours to obtain acompact. This compact was worked into a disc and a light-emitting diodeshown in FIG. 2 was fabricated. The thickness of the disc was adjustedso that the light-emitting diode could emit light having the same coloras that in Example 2. The thickness of the disc determined in this waywas almost the same as the thickness of the ceramic composite materialdisc of Example 2. The color of the light-emitting diode had CIEchromaticity coordinates of x=0.27 and y=0.36. The radiation energy ofthe thus-fabricated light-emitting diode was measured in the range from380 to 780 nm by using an integrating sphere. Also, the radiation energyof the light-emitting diode of Example 2 was measured in the samemanner. FIG. 10 shows the obtained light emission spectra of these whitelight-emitting diodes. As a result, the radiation energy of Example 2was about 1.5 times that of Comparative Example 1. This reveals that theceramic composite material for wavelength conversion of the presentinvention can transmit a larger quantity of light and can produce ahigh-brightness light-emitting diode.

INDUSTRIAL APPLICABILITY

The ceramic composite material for light conversion of the presentinvention is excellent in brightness, light mixing property, heatresistance and ultraviolet resistance. In particular, the ceramiccomposite material for light conversion of the present invention isexcellent in the performance of obtaining white light from blue lightand therefore, has a high practical value as a light source forillumination by making good use of the low power-consumption and longlife of a light-emitting diode.

1. A light conversion member having a unitary body consisting of aceramic composite material, said ceramic composite material being asolidified body comprising two or more matrix phases with respectivecomponents being two or more oxides selected from the group consistingof metal oxides and complex oxides each produced from two or more metaloxides, and at least one of said matrix phases being a phosphor phasecomprising an activated oxide.
 2. The light conversion member as claimedin claim 1, wherein said ceramic composite material comprises a matrixphase capable of being excited by visible light and emittingfluorescence of visible light at a wavelength longer than the excitationwavelength.
 3. The light conversion member as claimed in claim 1 or 2,wherein said ceramic composite material converts blue light into whitelight.
 4. The light conversion member as claimed in claim 1 to 3,wherein the solidified body is obtained by the unidirectionalsolidification method.
 5. The light conversion member as claimed inclaim 4, wherein respective matrix phases are continuously andthree-dimensionally disposed and entangled with each other.
 6. The lightconversion member as claimed in claim 1, wherein the metal oxide isselected from the group consisting of Al₂O₃, MgO, SiO₂, TiO₂, ZrO₂, CaO,Y₂O₃, BaO, BeO, FeO, Fe₂O₃, MnO, CoO, Nb₂O₅, Ta₂O₅, Cr₂O₃, SrO, ZnO,NiO, Li₂O, Ga₂O₃, HfO₂, ThO₂, UO₂, SnO₂ and rare earth element oxides(La₂O₃, Y₂O₃, CeO₂, Pr₆O₁, Nd₂O₃, Sm₂O₃, Gd₂O₃, Eu₂O₃, Tb₄O₇, Dy₂O₃,Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃ and Lu₂O₃).
 7. The light conversion member asclaimed in claim 1, wherein the complex oxide produced from acombination of two or more metal oxides is selected from the groupconsisting of 3Al₂O₃.2SiO₂ (mullite), MgO.Al₂O₃, Al₂O₃.TiO₂, BaO.6Al₂O₃,BaO.Al₂O₃, BeO.3Al₂O₃, BeO.Al₂O₃, 3BeO.Al₂O₃, CaO.TiO₂, CaO.Nb₂O₃,CaO.ZrO₂, 2CoO.TiO₂, FeAl₂O₄, MnAl₂O₄, 3MgO.Y₂O₃, 2MgO.SiO₂, MgCr₂O₄,MgO.TiO₂, MgO.Ta₂O₅, MnO.TiO₂, 2MnO.TiO₂, 3SrO.Al₂O₃, SrO.Al₂O₃,SrO.2Al₂O₃, SrO.6Al₂O₃, SrO.TiO₃, TiO₂.3Nb₂O₅, TiO₂.Nb₂O₅, 3Y₂O₃.5Al₂O₃,2Y₂O₃.Al₂O₃, 2MgO.2Al₂O₃.5SiO₂, LaAlO₃, CeAlO₃, PrAlO₃, NdAlO₃, SmAlO₃,EuAlO₃, GdAlO₃, DyAlO₃, Yb₄Al₂O₉, Er₃Al₅O₁₂, 11Al₂O₃.La₂O₃,11Al₂O₃.Nd₂O₃, 11Al₂O₃.Pr₂O₃, EuAl₁₁O₁₈, 2Gd₂O₃.Al₂O₃, 11Al₂O₃.Sm₂O₃,Yb₃Al₅O₁₂, CeAl₁₁O₁₈ and Er₄Al₂O₉.
 8. The light conversion member asclaimed in claim 1, wherein the phases constituting the matrix are twophases of α-Al₂O₃ phase and Y₃Al₅O₁₂ phase.
 9. The light conversionmember as claimed in claim 1, wherein said light conversion member is aplate member.
 10. A light-emitting diode comprising a light-emittingdiode chip, an electrode for supplying an electric current to thelight-emitting diode chip, and a light conversion member disposed on thelight emission side of the light-emitting diode for converting the colorof light emitted from the light-emitting diode chip into a differentcolor, wherein said light conversion member consists of a body of aceramic composite material body for light conversion which comprises twoor more matrix phases with respective components being two or moreoxides selected from the group consisting of metal oxides and complexoxides each produced from two or more metal oxides and in which at leastone of said matrix phases is a phosphor phase comprising an activatedoxide.
 11. The light-emitting diode as claimed in claim 10, wherein saidceramic composite material for light conversion comprises a matrix phasecapable of being excited by visible light emitted from thelight-emitting diode chip and emitting fluorescence of visible light ata wavelength longer than the excitation wavelength.
 12. Thelight-emitting diode as claimed in claim 10 or 11, wherein said ceramiccomposite material for light conversion converts blue light emitted fromthe light-emitting diode chip into white light.
 13. The light-emittingdiode as claimed in claim 10, wherein the solidified body is obtained bythe unidirectional solidification method.
 14. The light-emitting diodeas claimed in claim 13, wherein respective matrix phases arecontinuously and three-dimensionally disposed and entangled with eachother.
 15. The light-emitting diode as claimed in claim 10, wherein themetal oxide is selected from the group consisting of Al₂O₃, MgO, SiO₂,TiO₂, ZrO₂, CaO, Y₂O₃, BaO, BeO, FeO, Fe₂O₃, MnO, CoO, Nb₂O₅, Ta₂O₅,Cr₂O₃, SrO, ZnO, NiO, Li₂O, Ga₂O₃, HfO₂, ThO₂, UO₂, SnO₂ and rare earthelement oxides (La₂O₃, Y₂O₃, CeO₂, Pr₆O₁, Nd₂O₃, Sm₂O₃, Gd₂O₃, Eu₂O₃,Tb₄O₇, Dy₂O₃, Ho₂O₃, Er₂O₃, Tm₂O₃, Yb₂O₃ and Lu₂O₃).
 16. Thelight-emitting diode as claimed in claim 10, wherein the complex oxideproduced from a combination of two or more metal oxides is selected fromthe group consisting of 3Al₂O₃.2SiO₂ (mullite), MgO.Al₂O₃, Al₂O₃.TiO₂,BaO₆Al₂O₃, BaO.Al₂O₃, BeO.3Al₂O₃, BeO.Al₂O₃, 3BeO.Al₂O₃, CaO.TiO₂,CaO.Nb₂O₃, CaO.ZrO₂, 2CoO.TiO₂, FeAl₂O₄, MnAl₂O₄, 3MgO.Y₂O₃, 2MgO.SiO₂,MgCr₂O₄, MgO.TiO₂, MgO.Ta₂O₅, MnO.TiO₂, 2MnO.TiO₂, 3SrO.Al₂O₃,SrO.Al₂O₃, SrO.2Al₂O₃, SrO.6Al₂O₃, SrO.TiO₃, TiO₂.3Nb₂O₅, TiO₂.Nb₂O₅,3Y₂O₃.5Al₂O₃, 2Y₂O₃.Al₂O₃, 2MgO.2Al₂O₃.5SiO₂, LaAlO₃, CeAlO₃, PrAlO₃,NdAlO₃, SMAlO₃, EuAlO₃, GdAlO₃, DyAlO₃, Yb₄Al₂O₉, Er₃Al₅O₁₂,11Al₂O₃.La₂O₃, 11Al₂O₃.Nd₂O₃, 11Al₂O₃.Pr₂O₃, EuAl₁₁O₁₈, 2Gd₂O₃.Al₂O₃,11Al₂O₃.Sm₂O₃, Yb₃Al₅O₁₂, CeAl₁₁O₁₈ and Er₄Al₂O₉.
 17. The light-emittingdiode as claimed in claim 10, wherein the phases constituting the matrixare two phases of α-Al₂O₃ phase and Y₃Al₅O₁₂ phase.
 18. Thelight-emitting diode as claimed in claim 10, wherein said lightconversion member is a plate member.
 19. A light conversion methodcomprising converting the color of light emitted from a light-emittingdiode chip into a different color by using the light-emitting diodeclaimed in claim
 10. 20. The light conversion method as claimed in claim19, wherein blue light is converted into white light by using a ceramiccomposite material for light conversion in which the phases constitutingthe matrix are an α-Al₂O₃ phase and a Y₃Al₅O₁₂ phase and the Y₃Al₅O₁₂phase is a phosphor activated with cerium.